MxU networking architecture is known in the art and is used to provide communication services to a site (e.g., an apartment building) which includes a plurality of substantially independent sections (e.g., a plurality of apartments), each associated with a different subscriber. In general, the MxU networking architecture defines a separate local area network (LAN) for each of the sections.
MxU networks which are based Home Phoneline Networking Alliance (HPNA), use the telephone lines of the telephone wire network, already installed in the MxU. Each of the LANs includes the telephone wires which are associated with a selected section (e.g., apartment) and a plurality of HPNA nodes coupled with the telephone outlets. Telephone network voice communication and data communication services can be used simultaneously, using a technique known as frequency division multiplexing (FDM). Accordingly, data signals are transmitted using a different (higher) frequency than voice data signals, whereby these signals, can be separated using a frequency splitter.
A common problem in communication networks in general and MxU networks in particular, is interference between signals transmitted on adjacent communication lines, also known as crosstalk. Crosstalk is especially problematic when it is induced by a transmitter, transmitting over a communication line, to a nearby receiver which receives signals from an adjacent communication line. This type of crosstalk is known as near-end crosstalk (NEXT).
Methods and systems for reducing crosstalk in a network are known in the art. One conventional method for reducing NEXT is to use frequency division to separate between potentially interfering signals. Accordingly, signals transmitted in the upstream direction (i.e., from the user to the Central Office of the service provider) are transmitted using a different frequency than the signals transmitted in the downstream direction. For example, ADSL uses a lower frequency band for upstream communication and a higher frequency band for downstream communication.
Time division multiplexing (TDM) is a method, known in the art for preventing crosstalk between two different services (e.g., ISDN and ADSL). In a network using TDM, timeslots are defined for specific types of transmission and reception. For example, a certain timeslot may be allocated for transmission by one service, and a second timeslot for another service, whereby these transmissions do not interfere there between.
U.S. Pat. No. 5,991,311, entitled “Time-Multiplexed Transmission on Digital-Subscriber Lines Synchronized to Existing TCM-ISDN for Reduced Cross-Talk”, issued to Long et al., is directed to a data-service-line (DSL) system for installing together with an existing Integrated Services Digital Network (ISDN) system, wherein the ISDN system uses time-compression multiplexing (TCM). The DSL system also uses TCM. This enables synchronizing the TCM-DSL system and the TCM-ISDN system, using a clock. All of the TCM-ISDN line cards and the TCM-DSL line cards of the central office, transmit during a first time window, and receive during a second time window.
Reference is now made to FIGS. 1A and 1B. FIGS. 1A and 1B schematically illustrate an apartment building network, generally referenced 10, which is known in the art. FIGS. 1A and 1B show a first and second example of NEXT in an MxU network, respectively. It is noted that FIGS. 1A and 1B are not drawn to scale.
With reference to FIG. 1A, apartment building network 10 includes intra-apartment networks APT1 (referenced 121), APT2 (referenced 122) and APTN (referenced 12N), gateways G1 (referenced 221), G2 (referenced 222) and GN (referenced 22N), and telephone twisted-pair wires 241, 242 and 24N. A telephone wire binder 18 runs from a basement 14 of the apartment building, to the vicinity of intra-apartment networks 121, 122 and 12N. A platform 16 is located in basement 14. Gateways 221, 222 and 22N are mounted on platform 16. A broadband source 20 couples each of gateways 221, 222 and 22N with a wide area network (WAN) such as the Internet, via a broadband link such as xDSL, cable, fiber-optic, satellite, Local Multipoint Distribution System (LMDS), and the like.
Each of intra-apartment networks 121, 122 and 12N includes several network nodes (not shown), as shall be described in further detail with reference to FIG. 1C. Each one of gateways 221, 222 and 22N is coupled with a respective one of intra-apartment networks 121, 122 and 12N, via respective telephone wires 241, 242 and 24N. Each combination of one of the gateways 221, 222 and 22N, the respective one of the telephone wires 241, 242 and 24N, and the respective one of intra-apartment networks 121, 122 and 12N, together form a respective one of local-area networks (LANs) 151, 152 and 15N. Telephone wires 241, 242 and 24N are bound together in binder 18.
Gateway 221 transmits a data signal 26 to intra-apartment network 121. Simultaneously, intra-apartment network 122 transmits another data signal 28 to gateway 222. In a region 32, located in the vicinity of platform 16, an electrical disturbance 30, associated with data signal 26 (from telephone wire 241), is induced in telephone wire 242, causing an interference in data signal 28.
It is noted that conventionally, the distance between intra-apartment network 122 and region 32 is significantly greater than the distance between gateway 221 and region 32. Therefore, data signal 28 undergoes a significantly greater attenuation than data signal 26, before these data signals reach region 32, and hence, electrical disturbance 30 may cause a significant interference in data signal 28. This effect is known as near-end crosstalk (NEXT). It is noted that the transfer of disturbance 30 from telephone wire 241 to telephone wire 242 is a cumulative effect, which takes place all along wires 241 and 242, with a primary contribution occurring in region 32.
With reference to FIG. 1B, gateway 221 transmits a data signal 50 to intra-apartment network 121. Simultaneously, intra-apartment network 122 transmits another data signal 52 to gateway 222. In a region 56, located in the vicinity of intra-apartment networks 121 and 122, an electrical disturbance 54, associated with data signal 52 (from telephone wire 242), is induced in telephone wire 241, causing an interference in data signal 50.
It is noted that conventionally, the distance between gateway 221 and region 56 is significantly greater than the distance between intra-apartment network 121 and region 56. Therefore, data signal 50 undergoes a significantly greater attenuation than data signal 52, before these data signals reach region 56, and hence, electrical disturbance 54 may cause a significant interference in data signal 50.
Reference is further made to FIG. 1C, which is an illustration in detail of intra-apartment networks 121 and 122 of apartment building network 10 (FIGS. 1A and 1B) and a portion of the binder 18. FIG. 1C shows a third example of NEXT. It is noted that FIG. 1C is not drawn to scale.
Intra-apartment network 121 includes network nodes 801, 802 and 803. Nodes 801, 802 and 803 are coupled there between via telephone wire 241. Intra-apartment network 122 includes nodes 821 and 822. Nodes 821 and 822 are coupled there between via telephone wire 242.
Gateway 222 (FIG. 1A) transmits a data signal 86, through telephone wire 241, toward intra-apartment network 122. Simultaneously, node 801 transmits another data signal 88 toward node 802.
It is noted that conventionally, data signal 88 includes a header with source and target attributes. All of the nodes of LAN 151 (FIG. 1A) receive data signal 88, but only the target node, which is specified in the source-target attributes (i.e., node 802) addresses and decodes the data signal. It is noted that in the description that follows and the accompanying drawings, except for the present example, data signals are only shown on their path to their intended receiving node.
Data signal 88 passes through telephone wire 24, toward binder 18. In a region 84 in the vicinity of intra-apartment networks 121 and 122, an electrical disturbance 92, associated with data signal 88 (from telephone wire 241), is induced in telephone wire 242, causing an interference in data signal 86. Similarly as in the example set forth in FIGS. 1A and 1B, electrical disturbance 92 may cause a significant interference in data signal 86.